Given the high prevalence of school violence, it is necessary to develop actions aimed at preventing the problem and creating school contexts more effective in promoting prosocial behaviors from an early age. For this, it is important to carry out needs assessment studies. These are located in the prevention research cycle, at the stage of interventions development studies, having as one of its purposes the identification of difficulties and resources, in order to design a future strategy. Considering the above, the aim of this study was to conduct a needs assessment related to prosocial behavior promotion in preschool children, in order to prevent school violence. This is a mixed methods evaluative study, that included a sample of four teachers and 67 children from a public preschool, located in a city in southeastern São Paulo. To collect data, there were used an observation form to register teacher's practices related to prosocial behavior promotion, an observation form to register occurrence of prosocial behaviors among children, an inventory aimed at access teachers' educational social skills (IHSE-Prof), data extraction forms of weekly plans and bimonthly teacher planning, a semi-structured interview guide and a discussion focus group guide. A pilot study was conducted with a teacher and her class from another period of the school in order to refine proposed procedures. Data from each source underwent specific treatments and were submitted to descriptive analyzes. Resources and difficulties were detected for prosocial behavior promotion and violence prevention in the participating school. Resources include the existence, in teachers' repertoire, of practices that potentially promote prosocial behavior, some of them being more varied and others less, the presence of prosocial behaviors in children repertoires, a comprehensive understanding of preschool education mission, by most of the teachers, and teachers' favorable opinion in what concerns to the development of a future intervention in the school. Difficulties include teacher training gaps, lack of support for practice, repertoire of educational social skills to be developed, less understanding about the attributes of the preschool teacher, inconstantly planning and few planned content related to the promotion of prosocial behavior and social skills, and the perception that violence expressed in school only results from events occurred outside the institution. Thus, findings from the present study offer elements for the discussion about the process of schooling in the participating preschool and in the city where the institution is located, as well as have implications for the redirection of actions related to teaching, and provide subsidies for decision making of actions aimed at promoting prosocial behavior and preventing violence in schools.